Conde McCullough, Oregon's state bridge engineer, designed several concrete arch highway bridges in the 1920s and 1930s.

The Willamette River bridge between Oregon City and West Linn was one of the first. An old wooden suspension bridge, built in 1888, could not accommodate traffic on the new Pacific Highway that stretched from Canada to Mexico.

McCullough studied the site for two years and settled on a steel arch with the roadway suspended between two 350-foot arch ribs.

McCollough used the old suspension bridge's anchors, tower, and main cables to raise segments of the new bridge into place, then built the columns and hangers that support the roadway deck.

Finally, all of the exposed steel was covered in a concrete covering called Gunite, a combination of sand and cement that was mixed with water and air-blown onto the steel surfaces.

Gunite was used instead of paint, which would be eaten away by the corrosive fumes from nearby paper mills.